1. Field of the Invention
This invention relates to gas turbines in general, but more specifically to the interface region between a transition duct and a support bracket assembly.
2. Description of Related Art
In a typical land-based gas turbine engine, a plurality of combustors is positioned in a circular array about the engine such that each combustor delivers hot combustion gases to the turbine. The hot combustion gases are transferred to the turbine through a transition duct. The transition duct, at its inlet end is positioned adjacent the combustor exit by a support bracket. An example of a transition duct inlet and support bracket of the prior art is shown in FIG. 1. Due to the vibrations experienced by the combustion system and adjacent transition duct, frictional contact at the interface region between a support bracket and transition duct has been known to create excessive wear, especially on the support bracket, resulting in premature repair or replacement of the support bracket. To counteract the excessive wear, multiple embodiments of replaceable sleeves of harder material were developed for the fingers of the support bracket.
A first embodiment of a sleeve of the prior art is shown in FIGS. 2 and 3. FIG. 2 shows a top view of a support bracket 20 having sleeves 21, where sleeves 21 encompass all sides of bracket fingers 22. Referring to FIGS. 3A-3C, sleeve 21 is shown in detail. While the sleeve tends to reduce wear to the support bracket fingers, it is a complex assembly with respect to manufacturing. In order to manufacture this configuration, a half sleeve must be cut-out in a flat pattern and complex forming dies are then used to form the halves of the sleeve from the flat pattern. Next the two halves are welded together along joints 23, such that sleeve 21 will encompass all sides of fingers 22. The two halves are then welded together according to strict dimensional tolerances to avoid a loose-fitting sleeve. Finally, heat treatment of weld joints 23 occurs to relieve stresses in the welds, to prevent cracking. As a result of this extensive manufacturing process, the cost of this sleeve design is expensive, often as much as 25%-35% of the support bracket cost.
A second embodiment of a sleeve of the prior art is shown in FIGS. 4 and 5. FIG. 4 shows a support bracket 30, sleeve 31, support bracket fingers 32, and transition duct mounting block 33. As with the first embodiment of the prior art, sleeve 31 is designed to protect fingers 32 from excessive wear due to contact with mounting block 33. The critical surfaces of fingers 32 to protect are those that are in contact with corresponding surfaces of mounting block 33. As it can be seen in FIG. 4, this second embodiment does not protect all of the desired surfaces of fingers 32. Specifically, the underside surface 34 is left exposed and unprotected from mounting block 33. Furthermore, as with the first sleeve embodiment, the second embodiment also requires complex manufacturing techniques to prepare a sleeve in a flat pattern, then form it into the final shape as shown in FIG. 5.
While each of these prior art embodiments have reduced the amount of wear experienced on some surfaces of a transition duct support bracket, neither embodiment provides complete wear reduction capability on all critical surfaces, while being cost efficient to manufacture.